Ch. 2.3 Viruses

What are viruses? Viruses are nonliving. They are a strand of hereditary material (DNA), surrounded by a protein coat. They do not have a nucleus, organelles, or cell membranes. Many viruses cause diseases like cold sore, measles, chicken pox, the flu, and AIDS.

How do viruses multiply? All viruses can do is make copies of themselves. They must have a host cell – a living cell There are 2 types of viruses: active or latent

Active Viruses An active virus uses the host cell to make new viruses and then destroys the host cell.

Latent Viruses After a latent virus infects a host cell its DNA becomes part of the host cell’s DNA. Every time the host cell replicates it also replicates the viral DNA. Certain conditions can cause the virus to become active. Example: cold sores

How do viruses affect organisms? Viruses attack the organisms they infect. Viruses can be very species or cell specific. Example: a virus that infects a dog can only infect the dog. Sometimes viruses can affect different species – like rabies.

Viruses that infect bacterial cells are called bacteriophages.

Fighting Viruses Vaccines help prevent viruses. A vaccine is made from a weakened or dead virus that can’t cause the disease anymore. Vaccines have been made to prevent disease like measles, mumps, smallpox, chickenpox, polio, rabies, and the common flu.

The first vaccine Edward Jenner in 1796 made the first vaccine. It was a vaccine for smallpox.

Treating Viral Diseases Antibiotics do not treat viral diseases. They only treat bacterial diseases. Your body stops viruses by making interferon's. These are proteins that are made by infected cells but move to non- infected cells. The non-infected cells can fight the virus.

Viruses, in rare cases, can be helpful. One way is in gene therapy Viruses, in rare cases, can be helpful. One way is in gene therapy. Viruses can be used to help insert a gene into a cell.